Method and apparatus for applying horizontal markings to roads or other traffic areas

ABSTRACT

In the method for applying horizontal markings to road surfaces, a water-thinnable emulsion paint which is acid-coagulable is used and is brought into contact with an acid. This acid is scattered or sprayed onto or into the sprayed paint, the acid being in the form of an aqueous solution, a powder or particles wetted with acid. The method brings about drying within one or a few minutes. Using road-marking vehicles, horizontal markings can thus be put down with virtually no closing-off of the mobile operations site.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and to an apparatus forapplying horizontal markings to roads or other traffic areas, usingwater-thinnable emulsion paints.

2. Description of the Related Art

Horizontal markings, especially limiting, guiding and warning lines, aregenerally applied using a marking vehicle which is equipped with paintspray guns for spraying the marking paint and, optionally, with beadscatterers for applying reflective beads, as described, for example, inEP-B-0 280 102.

Marking paints containing solvents are known generally, but their use isbeing increasingly criticized for reasons of environmental protection.Also known are water-thinnable emulsion paints, which are moreenvironmentally friendly.

A disadvantage common to both types of marking paints, however, is afairly long drying time, of in general from 10 to 30 minutes. At adrying time of, for example 20 minutes and a marking rate of 6 km/h,therefore, it is necessary to close off a stretch of 2 km at a timebehind the operations site with the aid of a blocking gang, resulting inconsiderable hindrances and hold-ups for traffic. Furthermore, markingwork has to be interrupted in inclement weather and when rain threatens,so as to avoid the possible running of paint which has not yet becomewater resistant.

EP-A-0 200 249 describes a process in which an aqueous emulsion paint iscaused to dry within 15 minutes--in specific cases in 6 minutes--afterapplication, by the addition of a water-soluble salt, for example sodiumchloride, calcium chloride or the like. The quantity of salt is fromapproximately 15 to 25 g per m² of painted surface.

EP-A-0 409 459 describes acid-coagulable emulsion paints which contain,in particular, an anionic stabilized polymer emulsion and apolyfunctional amino polymer and which are stabilized in the alkalinerange by a volatile base. After application the base evaporates, so thatthe pH falls and, as it passes the pH of coagulation, the paintsolidifies. The drying time is from 10 to 20 minutes or more, dependingon the temperature and the degree of atmospheric humidity, which arefactors which affect the evaporation of the base.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide a method and an apparatuswhich together permit marking work to be carried out with shorter paintdrying times, which are largely independent of the weather, and whichtherefore make it possible to work even in unfavourable weatherconditions, irrespective of atmospheric humidity and temperature, andwith virtually no closure of the road.

This object is achieved, with respect to the method, by the featuresspecified in the characterizing clause of claim 1 and, with respect tothe apparatus, by the features indicated in claim 9.

The application of the paint and of the acid is carried out by methodswhich are well known to the person skilled in the art, preferably byspraying.

The invention makes it possible to shorten the drying time of the paint,and with it the time before it is possible to drive--in the road-trafficsense--over the paint to only from about one to two minutes or evenless, depending on the coat thickness and application method, and thusto a fraction of the drying times which were previously required.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in more detail, with reference to thedrawings, by exemplary embodiments. In the drawings

FIG. 1 shows a first example of a marking vehicle (which is only vaguelyindicated) with a paint spray gun, a reflective-bead scatterer and anozzle for spraying acid on to the marking,

FIG. 2 shows a second example, in which the acid is sprayed directlyinto the jet of paint,

FIG. 3 shows a third example, in which a bead scatterer scattersreflective beads, which have been treated beforehand with acid, into thejet of paint,

FIG. 4 shows a fourth example, in which the installations illustrated inFIG. 1 on the marking vehicle are supplemented by further installations,and

FIGS. 5 and 6 show tables of the results of comparative tests.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

According to a first embodiment of the method according to theinvention, which can be carried out with a marking vehicle moving in thedirection of the arrow in accordance with FIG. 1, the fresh film ofpaint applied is sprayed, shortly after application, with an aqueoussolution of an acid. For this purpose the marking vehicle 1 carries aconventional paint spray gun 2, which sprays a jet 3 of paint on to theroadway S, followed by a bead scatterer 6, which scatters reflectivebeads 7 on to the fresh marking, and followed in turn by a nozzle 4 forspraying an acid 5 on to the freshly sprayed paint marking.

In a second embodiment, acid solution is applied, as shown in FIG. 2,simultaneously with the paint, by the acid 5 being sprayed into thespray mist of the paint 3, which comes from a spray gun 2, from a spraynozzle 4 which is installed directly following said spray gun 2. Thisachieves a homogeneous distribution of the acid in the coat of paint,and a homogeneous coagulation and thus solidification of the paint.Subsequently the bead scatterer 6 applies reflective beads 7 to thefresh marking.

In accordance with a third embodiment, the acid is used in the form ofan acid-containing powder or of an acid-containing particulate material.For this purpose, for example, solid acid is mixed and ground withvarious commercially available fillers (e.g. silicates, sulphates, metaloxides) until the desired particle size and proportion are reached.

According to a preferred embodiment an acid-containing material isprepared as follows: water-soluble acid is dissolved in water,reflective beads in the form of glass beads are added to the solution,conventional fillers and/or binders are added if required, and themixture is filtered and allowed to dry. In this way the glass beads arecoated with acid. It is also possible to coat and to use other,so-called profiled particles; this combined application of paint andglass beads or other particles is carried out as described, for example,in EP-0 280 102. In this case the glass beads are used, on the one hand,for the rapid drying of the paint on application, and thereafter asreflection media on the road marking. The entire operation can becarried out by traversing the stretch to be worked on a single time,after which the mobile operations site is moved on.

The abovementioned embodiment of the method can be carried out using amarking vehicle 1 as shown in FIG. 3; in this case the paint spray gun 2sprays a jet 3 of paint on to the road surface S, and a bead scatterer 8scatters glass beads 9 into the jet 3 of paint emerging from the spraygun 2, the glass beads 9 having been treated beforehand, as describedabove, with an acid 5. Instead of treated reflective beads it is alsopossible to scatter other particles treated with acid, especiallyprofiled particles, into the jet 3 of paint. In one variant of themethod, the acid-treated reflective beads or other particles can also bescattered on to the freshly drawn road marking after the application ofthe paint to the road surface S. In addition, in the example accordingto FIG. 5, a rear bead scatterer 6 is also provided, for applying normalreflective beads 7 by scattering.

In relation to the known method, which is described in EP-B-0 280 102,the novel method according to the invention can be employed as follows,using, for example, a marking vehicle according to FIG. 4:

A marking vehicle 1 carries, following one another at short distances, apaint spray, gun 2, a particle dispenser 10, a nozzle 4, a second paintspray gun 12, a bead scatterer 6 and a second nozzle 13. The spray gun 2sprays a jet 3 of paint on to the roadway surface S, following which theparticle dispenser 10 applies profiled particles 11 to the marking; ashort way behind this the nozzle 4 sprays acid 5 on to the fresh roadmarking, after which the profiled particles are covered with paint bymeans of the jet 3 of paint sprayed from the second paint spray gun 12;normal reflective beads 7 are then applied using the bead scatterer 6,and adhere in particular to the raised paint profiles produced by theprofiled particles 11; finally, for the rapid drying of the film ofpaint ultimately applied, the nozzle 13 again sprays acid 5 on to themarking.

The method according to the invention can be carried out usingcommercially available, water-thinnable, acid-coagulable paintdispersions. The suitability of a particular dispersion for the methodcan be tested very easily: an acid is slowly added dropwise to thedispersion and, if the dispersion coagulates very quickly after acertain level of addition, it is suitable. Numerous acid-coagulable,water-thinnable dispersions or emulsions which can be used in accordancewith the present method are described in EP-A-0 409 459. The pH of theformulations is adjusted to a pH of from 8 to 10 by means of known basessuch as, for example, sodium hydroxide solution, ammonia and/or primaryto tertiary organic amino bases, In contrast to EP-A-0 409 459, however,the use of volatile bases is not necessary according to the presentinvention. The solidification of the formulation (coagulation) occurs ingeneral as it suddenly changes to a weakly acidic pH.

Most of the commercially available organic and inorganic, volatile ornonvolatile acids can be used in accordance with the present method inthe form of an aqueous or, if possible, an organic solution, for exampleacetone. Examples are hydrochloric acid, sulphuric acid, phosphoricacid, nitric acid, acetic acid and citric acid.

Instead of acids it is also possible to use acid anhydrides, which reactas acid on contact with the water of the aqueous emulsion paint. The useof appropriate anhydrides of inorganic acids, for example phosphoruspentoxide in solid form, or appropriate anhydrides of organic acids, insolid or liquid form, for example acetic anhydride dissolved in water orin an organic solvent such as acetone, have also given good results.When solid acid anhydrides are employed, they are preferably used inpowder form and either scattered into the jet of paint from the spraygun or scattered on to the fresh paint marking, or alternatively usedfor coating reflective beads or profiled particles.

Aqueous acetic acid and citric acid have proved to be particularlyadvantageous, since acetic acid is volatile, environmentally friendlyand inexpensive and because citric acid is odourless.

In the case of weak acids such as citric and acetic acid, a from 10 to30 per cent strength, preferably an approximately 20 per cent strength,aqueous acid solution is used, whereas in the case of stronger acidssuch as hydrochloric or sulphuric acid a from 5 to 15 per cent strengthsolution, preferably an approximately 10 per cent strength solution isused. Relative to the methods which bring about solidification of thepaint by addition of salts, the quantities of acid required are muchlower. Depending on the nature and composition of the paint dispersionused, on the acid and the acid concentration and on the applicationmethod, an addition of dilute acid of from 0.6 to 2% by weight of thequantity of paint dispersion applied gives good results; in most casesabout 1% by weight has been sufficient.

Numerous tests have been carried out, in particular with paintformulations which contain not only the conventional components,especially fillers and colour pigments, but also the three followingcommercially available dispersions as binders:

Joncryl (trade mark), sold by Johnson;

Luhydran (trade mark), sold by BASF;

Primal (trade mark), sold by Rohm and Haas.

The acids tested were citric acid, acetic acid, hydrochloric acid andsulphuric acid.

The tables in FIGS. 5 and 6 show test results for the three formulationsindicated in column 1, in one case at a paint coat thickness ofapproximately 1000μ (FIG. 5) and in the other case at 400μ (FIG. 6). Thetest results relate on the one hand to laboratory experiments, in whichthe coat of paint was applied to a non-absorbent substrate in the formof a glass plate, and on the other hand to practical tests, in which thepaint dispersions indicated were applied to a conventional bituminousroad covering. In the laboratory tests the water content of the paintdispersions used was, as indicated, 45%, 27% and 18% respectively, andin the road tests it was 18%. The laboratory results obtained at thetemperature and atmospheric humidity values indicated in columns 2 and 3respectively are given in columns 4, 5, 6 and 7, the three minuteindications which appear in each case, separated by oblique strokes,relating to the abovementioned water contents of 45%, 27% and 18%respectively, i.e. with the water content decreasing across thesequence.

The pH of the formulations used was adjusted to from 9 to 10 with theabovementioned bases. The results obtained with different acids werevirtually identical and are therefore not listed individually. The dataindicated relate, in the case of the tests with a paint coat thicknessof 1000μ (FIG. 5), to 30 per cent strength aqueous citric acid, and to20 per cent strength acetic acid for a paint coat thickness of 400μ(FIG. 6). The quantities measured in each case were the times afterwhich the paint had dried and, respectively, had become water resistant,as indicated in columns 4 to 9 of the tables and expounded in moredetail below.

The laboratory experiments were carried out in still air in aclimatically controlled chamber. A drawing shoe was used to apply thepaint dispersions to a glass plate in a defined coat thickness. Directlythereafter the film of paint was sprayed with acid solution andsubsequently with acid until the paint coagulated. Drying was determinedwith a normal "thumb test", i.e. by applying the thumb with a slightrotation. If this did not damage the paint film, the paint wasconsidered to be dry and thus capable of being driven over. After dryinghad been determined the paint film was held for 15 seconds in runningwater: when it was no longer washed off under these conditions it wasregarded as being water resistant.

In the road tests, marking lines were drawn with a conventional paintspray gun. In the case of a paint coat thickness of 1000μ (FIG. 5) theacid solution was sprayed, using a marking vehicle according to FIG. 2,directly into the jet of paint coming from the paint spray pistol. Inthe case of a paint coat thickness of 400μ (FIG. 6) the acid solutionwas sprayed, using a marking vehicle according to FIG. 1, on to thefresh marking after the application of the paint. The drying times weredetermined as follows: a passenger car drove over the paint markingwhich had been put down. The paint was considered to be dry when therewere no traces of paint to be seen on the tire of the car, or when therewere no tire marks on the paint. The paint marking was regarded as waterresistant if it did not become detached after 10 seconds under runningwater.

In the road tests, within the margins of error, approximately the same,short times indicated were obtained for all temperatures and all valuesof atmospheric humidity: at a paint coat thickness of 1000μ the dryingtime was 2 minutes or less and the "water resistance" time was 3 minutesor less. In the case of a paint coat thickness of 400μ (FIG. 6) thedrying time was 3/4 minutes or less and the "water resistance" time was1.5 minutes or less. Even at other temperatures and atmospherichumidities, as indicated in FIG. 6, the changes in the drying timesindicated were quite insignificant.

The quantity of aqueous acid solution used was about 1% by weight of thequantity of pain applied.

The tables of FIGS. 5 and 6 show that the drying times when acid is usedare many times shorter than in the case of normal drying without acid.It is also evident that the drying times which were obtained in the openair, i.e. with air movement present virtually all the time, on aconventional more or less absorbent bitumen substrate are substantiallyshorter than the drying times obtained on a glass plate in aclimatically controlled chamber without air movement. As is to beexpected, the drying times using the same application technique but witha lower paint coat thickness are shorter than for a larger paint coatthickness. Also, the drying time decreases markedly as the water contentof the paint falls. Finally, the tables show that the times for dryingand for water resistance without the addition of acid depend fairlyheavily on the atmospheric humidity and on the temperature, but arevirtually independent of temperature and atmospheric humidity when acidis added.

As was shown, the method can be carried out in all of the abovementionedembodiments, if the coat of paint applied has a thickness of less thanfrom 350μ to 450μ. At greater coat thicknesses it is advisable to applythe acid not only to the surface of the paint already applied, sinceotherwise there is a risk that a solid surface skin will form with thepaint remaining liquid underneath, but instead to apply the acid or theacid-containing material simultaneously with the paint, for example inthe form of a spray mist.

In practice a further procedure is first to apply the paint and,optionally, the glass beads with a conventional marking vehicle whileapplying the acid by spraying from a safeguarding vehicle which directlyfollows the marking vehicle, such a safeguarding vehicle normally beingused in mobile operations sites and carrying warning and direction signsfor the traffic behind.

The invention therefore provides a cost-effective method for bringing aroad marking rapidly to a state where it can be driven over. The methodcan be-employed on any mobile operations site, on parking areas, onairport runways, etc., and in general on any civil engineeringconstruction site where there is a need to work very quickly. Anotherfeature worthy of note is the environmental compatibility of the method:since coagulation occurs even at a weakly acidic pH and the acid appliedis neutralized, virtually no acid passes on to the road and into theenvironment. In addition, if a nonvolatile acid, for example citricacid, is used, this method is also absolutely odourless.

The method according to the invention can be employed in the mannerdescribed to all aqueous paint formulations which are based on anacid-coagulable binder.

I claim:
 1. Methods of applying horizontal markings to roads or othertraffic areas, which comprises;applying to the area an aqueous,water-thinnable, acid-coagulable emulsion paint; and contacting theapplied paint with an acid.
 2. Method according to claim 1, wherein anemulsion paint is used which has been formulated to the basic and whichcontains an acid-coagulable binder.
 3. Method according to claim 1,wherein the acid is sprayed on to the applied emulsion paint.
 4. Methodaccording to claim 1, wherein the emulsion paint is sprayed on to thearea and the acid is sprayed into a spray mist of the paint duringapplication.
 5. Method according to claim 1, wherein an acid anhydrideis added to the emulsion paint and forms acid.
 6. Method according toclaim 5, wherein the acid anhydride is selected from the groupconsisting ofanhydrides of inorganic acids and anhydrides of organicacids.
 7. Method according to claim 1, wherein the acid is in the formof solid, acid-containing or anhydride-containing particles which arescattered on to the applied emulsion paint.
 8. Method according to claim7, wherein the acid-containing particles are composed of glass beadswhich are coated with a thin, adhering layer of solid acid or solid acidanhydride.
 9. Method according to claim 1, wherein the emulsion paint issprayed on to the area and the acid is in the form of solid,acid-containing or anhydride-containing particles which are sprayed intoa spray mist of the paint.
 10. Method according to one of claims 1,wherein the acids used are commercially available.
 11. The method ofclaim 1 wherein the acid is selected from the group consisting of a 10to 30 percent aqueous solution of a weak acid and a 5 to 15 percentaqueous solution of a strong acid.
 12. The method of claim 1 wherein thequantity of acid is 0.6 to 2.0 percent by weight of the paint. 13.Apparatus for applying a horizontal marking to a road or other trafficarea, which comprises;a vehicle (1); a spray gun mounted on the vehicle,in a position to spray marks on the area; and means for applying an acidto the spray marks, mounted on the vehicle.
 14. Apparatus according toclaim 13, wherein the vehicle (1) carries behind the spray gun (2) adispenser (10) for profiled particles (11), followed by areflective-bead scatterer.